Zinc sulfur battery

ABSTRACT

An electric storage cell ( 10 ) comprises a zinc anode ( 12 ) and a sulfur cathode ( 14 ), wherein the zinc and the sulfur are in contact with an aqueous solution ( 22 ) containing sulfur during the process of battery discharge. In this invention, specific conditions for the aqueous sulfur electrolyte are chosen to overcome the normal ineffectiveness of zinc oxidation in the presence of aqueous zero valent sulfur. Normally, a zinc anode ( 12 ) cannot be oxidized in an aqueous solution containing sulfur, because the product of the discharge would be zinc sulfide. This zinc sulfide is a highly insoluble salt and creates a layer which passivates the zinc and renders it completely ineffective to battery discharge. The performance of the battery is made possible by high OH- and HS-ion concentrations formed by the addition of salts to the aqueous zero valent sulfur solution, and permits effective and efficient battery discharge.

The present invention relates to batteries. More particularly, theinvention relates to electrical storage cells of the type having halfcells in operative electrochemical contact.

BACKGROUND OF THE INVENTION

There is an ongoing need for providing novel improved electrical storagebatteries, which are low-cost and high energy density. The two mostcommonly used types of batteries are the lead-acid battery as employedin automobiles and the dry cell as used in most flashlights. The lightweight of sulfur, makes sulfur-based batteries to be quite attractivefor electrochemical energy storage and accordingly a variety ofmetal-molten sulfur batteries are described in the literature. Hightemperature molten alkali sulfide batteries have been investigated, butserious problems were encountered with the high temperatures requiredfor maintaining a liquid phase, the electrical insulation, passivationof sulfur, as well as safety considerations.

Although less conductive than molten salts, the often toxic. oganosulfocathodes, such as discussed in the U.S. Pat. No. 4,833,048, usingmaterials of the general formula (R(S)_(y))_(n), where R is a chemicalcomponent containing from 1 to 20 carbon atoms, can be used as acathode, however the additional weight of the carbon will decrease theelectrical storage capacity. Recently, concentrated aqueous polysulfidesolutions were found to provide a medium for highly reversible twoelectrons redox chemistry at ambient temperature. In a paper by thepresent Inventor (Journal Electrochemical Society, 1987, 134, p.2137-41) aqueous sulfur redox cells were mentioned to possess a highfaradaic capacity. The cells are utilizing electrolytes which by theirmass could accommodate more reducible sulfur than water. In a laterpaper (Journal Electrochemical Society, 1993, 140, p. L4) the inventordescribes aluminum-sulfur batteries based on concentrated polysulfidecatholytes and an alkaline aluminum anode.

The present Inventor also described in his prior U.S. Pat. No. 4,828,942an aqueous sulfur cathode containing at least 20% by weight sulfur in abattery with a sulfide anode. The room temperature sulfur electrolyte,provides a conductive and reversible battery which possesses a highcapacity half-cell storage material. In 1993, the capacity of thecathode was further increased by the addition of solid sulfur, asdescribed by Peramunage and Licht, (Science, 1993, 261, p. 1029).According to the recent U.S. Pat. No. 5,424,147 (by Khasin) awater-activated, deferred-action battery is disclosed. The cathode ofthe battery is made from a skeletal frame which comprises cuprouschloride, sulfur, carbon and a water-ionizable salt, compacted and fusedunder pressure and heat. The sulfur in the cathode acts to improve thedischarge of the cuprous chloride, but the sulfur itself is notdischarged. The anode is selected from the group consisting of zinc,magnesium, aluminum and alloys thereof. Although this type of batteryhas an advantage by not using lead, known by its environmental problem,it suffers from a disadvantage connected with the manufacture of theskeletal frame of said cathode. From a storage capacity andenvironmental view, zinc is an attractive anode material which is usedin several batteries including dry cells. However, a zinc anode cannotbe oxidized in an aqueous solution containing sulfur, because theproduct of the discharge is zinc sulfide:

Zn+S²⁻→ZnS+2e⁻  (1)

The present Inventor determined than zinc sulfide was even less solublethan previously thought. (Journal Electrochemical Society, 1988, 135, p.2971) which would prevent dissolution, with a solubility product of10^(−25.4) given by:

ZnS_(solid,precipitate)Zn²⁺+S³⁻K_(sp)=10^(−25.4)=[Zn²⁺][S²⁻]  (2)

This zinc sulfide is a highly insoluble salt and creates a layer whichpassivates zinc and rendering it completely ineffective to batterydischarge.

It is an object of the present invention to provide a safe and reliablebattery, capable of producing high energy densities. It is anotherobjective of the invention is to provide a battery made of relativelyinexpensive materials.

BRIEF DESCRIPTION OF THE INVENTION

The invention relates to a novel type of battery which comprises twohalf-cells which are positioned in electrochemical contact with oneanother through an aqueous solution, wherein one or said half-cellscomprises a zinc anode and the second half-cell comprises an aqueoussolution of a concentrated metal cation hydrosulfide salt and areducible sulfur in a amount of at least 0.01 moles per kg, beingpositioned in an electron transferring contact with a currenttransferring electrocatalytic electrode. The discharge of the battery isbased on the oxidation of the zinc, which occurs despite the presence ofsulfur, by using a high concentration of hydrosulfide and hydroxide inthe solution.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: is a diagrammatic representation of a zinc sulfur battery.

FIGS. 2-5, correlate the discharge capacity (amp hours) of variouszinc-sulfur batteries at 50° C. as a function of cell voltage.

DETAILED DESCRIPTION OF THE INVENTION

The battery according to the present invention, is based on the use of azinc anode half cell with a sulfur half cell, including an aqueoussulfur solution containing a hydrosulfide and a hydroxide salt, incontact with an electron transferring electrocatalytic electrode whichsustains an electrochemical reduction of the dissolved sulfur. Thedischarge of the battery is based on the oxidation of the zinc, whichoccurs despite the presence of sulfur, by using a high concentration ofhydrosulfide and hydroxide in the solution.

The anode of the battery may consist of a low surface area as well as ahigh surface zinc. Among the low surface area it should be mentionedplanar sheet, rods, etc. Among the high surface area zinc, it should bementioned porous zinc, zinc screen, pressed zinc powder, etc. The zincmay be pure, or less pure (92% to 99%) either due to impurities oralloying. Among the impurities and alloy materials should be mentionedthose common to zinc including tungsten, cobalt, lead, copper, selenium,antimony, germanium, sulfur, iron, cadmium, nickel, manganese, tin andthe other known zinc allowing materials. The hydrosulfide salt may beselected from alkali hydrosulfide having the formula MHS, wherein M isan alkali cation to be obtained by the reaction of alkali hydroxide andhydrogen sulfide. The presence of high concentrations of the hydroxideor hydrosulfide will permit the zinc oxidation, despite the presence ofsulfur. According to the invention, without being bound to any theory,the oxidation reaction of zinc in sulfide electrolytes occurs asfollows:

Zn+HS⁻+OH⁻→ZnS+2e⁻+H₂O   (3)

It seems that in this reaction, the anion OH⁻ or HS⁻ will facilitate thezinc oxidation, despite the presence of sulfide. The sulfur cathodecontains sulfur, S, dissolved as a variety of polysulfide species, anddischarge of the sulfur cathode may be summarized:

S+H₂O+2e⁻→HS⁻+OH⁻  (4)

Without being bound to any theory, the oxidation reaction of zinc, insulfur electrolytes occurs according to the reaction:

Zn+S→ZnS E_(cell)=0.90 V   (5)

Moreover, a high capacity will be achieved due to zinc sulfide dischargeproduct. The faradaic capacity of the Zn/S battery based on 2 faraday ofcharge transfer per mole of Zn (65.38 g/mole) and sulfur (32.06 g/mole),is 550 Ah/kg, and the theoretical specific energy is 495 Wh/kg (0.90Volt×550 Ah/kg). Effective zinc oxidation, despite the presence ofsulfide, as well as the high capacity due to the zinc sulfide dischargeproduct, are the new advances which now permit demonstration of a viablezinc sulfur battery. The performance of the battery is enhanced byconditions of high OH⁻ and HS⁻ concentrations.

According to a preferred embodiment, the solution in said electrolytecontains more than 1 mole per kg of a hydrosulfide salt, wherein saidhydrosulfide is selected from the group consisting of alkali cations,alkali-earth cations, transition metal cations, cations of group IIIA,group IVA, group VA and Hydrogen. Typical examples of such hydrosulfidesalts include, but are not limited to, KHS, NaHS, LiHS, CsHS, RbHS, H₂S,Be(HS)₂, Mg(HS)₂, Ca(HS)₂, SrHS₂, HgHS, Hg(HS)₂, CuHS, CuHS₂, Zn(HS)₂,AgHS, Fe(HS)₂, Fe₂(FeO₄)₃, Mn(HS)₂, Ni(NS)₂, Co(HS)₂, Al(HS)₃, In(HS)₃,Ga(HS)₃, Sn(HS)₄, Sn(HS)₂, Pb(HS)₂. The solution also contains ahydroxide salt of an element selected from the group consisting ofalkali cations, alkali earth cations, transition metal cations andcations of group IIIA elements in an amount of above 1 mole per kg of ahydroxide salt. Typical examples of such hydroxide salts include, butare not limited to, KOH, NaOH, LiOH, CsOH, RbOH, H₂S, Be(OH)₂, Mg(OH)₂,CaOH₂, HgOH, Hg(OH)₂, CuOH, Cu(OH)₂, Zn(OH)₂, AgOH, Fe(OH)₂, Fe₂(FeO₄)₃,Mn(OH)₂, Ni(OH)₂, Co(OH)₂, Al(OH)₃, In(OH)₃, Ga(OH)₃, Sn(OH)₄, Sn(OH)₂,Pb(OH)₂, etc. In this preferred embodiment, the anode contains zincmetal which is capable to be oxidized. The solution contains alsodissolved sulfur which may be reduced upon discharge and contact with anelectrocatalytic electrode such as CoS.

In another preferred embodiment, the cell contains means to impededtransfer of the chemically reactive sulfur between said zinc anode andsulfur present in said other half cell. Examples of such means includes,but is not limited a membrane, ceramic frit, or agar solution to belocated in a position which separate the said half cells.

In another aspect of the invention, the cell may also be rechargeable byapplying a voltage in excess of the voltage as measured withoutresistive loads of the discharged, or partially discharged cell. Inanother embodiment, the cell also contains an excess of undissolvedsulfur.

By “discharge cell open circuit potential”, as used herein, is meant thevoltage, as measured without resistive load, of the discharged orpartially discharged cell.

Among the advantages of the present invention, it should be mentionedthe capability of a high electrical storage capacity with inexpensivematerials such as zinc and sulfur as well as the fact that the batterydoes not need to operate at high temperatures in order to obtain adischarge of sulfur.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a battery which is based upon zinc anodehalf cell and a sulfur half cell, including an aqueous sulfur solutioncontaining a hydrosulfide and a hydroxide salt, in contact with anelectron transferring electrocatalytic electrode sustainingelectrochemical reduction of dissolved sulfur. Discharge of the batteryis based on oxidation of the zinc occurring, despite the presence ofsulfur, by using concentrated hydrosulfide and hydroxide in solution.The zinc anode of the battery can consist of low surface area as well asa high surface zinc. The hydrosulfide salt, including, but not limitedto, alkali hydrosulfide salts in the form of, MHS, where M is a analkali cation, may be prepared by reaction of H₂S in an alkalinehydroxide solution according to the reaction:

H₂S+MOH→MHS+H₂O   (6)

High concentrations of KOH or KHS can permit zinc oxidation, despite thepresence of sulfur.

In FIG. 1, the cell (10) is a diagrammatic representation of anelectrochemical storage cell based on a sulfur half cell, anelectrically neutral ionic conductor (22) and a zinc anode (12). Theelectrically neutral ionic conductor (22) may be a concentrated solutionof aqueous KOH and KHS containing dissolved sulfur, in contact with anelectrocatalytic cathode (14) such as CoS. Reduction of sulfur ions suchas in the form of a polysulfide anions, is achieved via electrons whichare supplied by said electrode (4). The zinc anode electrode (12) suchas in the form of a metal, is also in contact with the electricallyneutral ionic conductor (22). During the oxidation of the anode,electrons are released. Optionally, the cell may contain an ionselective membrane (20), or a separator (20), for minimizing thenon-electrochemical interaction, or preventing electrical contact,between the cathode and the anode.

The invention will be hereafter illustrated by the following Examples,being understood that the Examples are presented only for a betterunderstanding of the invention without implying any limitation thereof,the invention being covered by the appended claims.

EXAMPLE I

High anodic current density is necessary to permit effective batterydischarge. According to the theory, and as seen in the followingExamples, a zinc sulfur battery would not be able to discharge in anaqueous polysulfide solution comprising polysulfide anions since thezinc sulfide product of the battery discharge is insoluble and notconductive. Also, this example illustrates that normally, a zinc anodecan not be oxidized in an aqueous solution containing sulfur. Thisexample also illustrates that normally, a zinc anode is easily oxidizedin an aqueous solution containing hydroxide. High anodic current densityis necessary to permit effective battery discharge.

TABLE 1 Normally dissolved sulfur solutions do not support zincdischarge currents. The oxidation current of planar 99.9% zincelectrodes is measured at various potentials in 2 molal K₂S₄ or 3 molalKOH, and at 22° C. or 75°. The cell potential, V_(cell), in units ofmillivolts, mV, is determined relative to a separate sulfur cathode.J_(Zn) is the oxidation current measured on a planar zinc electrode.Zinc in 2 molal K₂S₄ Zinc in 3 molal KOH T = 22° C. T = 75° C. T = 22°C. T = 75° C. V_(cell) J_(Zn) V_(cell) J_(Zn) V_(cell) J_(Zn) V_(cell)J_(Zn) mV mA/cm² mV mA/cm² mV mA/cm² mV mA/cm² 850 0.0 850 0.0 810 0.0920 0.0 750 0.0 750 0.0 770 10.0 880 10.0 650 0.0 650 0.0 740 20.0 85020.0 550 0.0 550 0.0 710 30.0 820 30.0 450 0.0 450 0.0 685 40.0 795 40.0350 0.0 350 0.0 665 50.0 775 50.0 250 0.0 250 0.0 645 60.0 755 60.0 1500.0 150 0.0 625 70.0 735 70.0 100 0.0 100 0.0 605 80.0 715 80.0 50 0.050 0.0 580 90.0 695 90.0 0 0.0 0 0.0 560 100.0 670 100.0

A planar zinc electrode was inserted in an aqueous solution whichcontained potassium hydroxide (3 molal) facilitating anode discharge(zinc oxidation) at a high current density of 100 mA/cm², the anodicpotential being enhanced by increasing the temperature from 25° C. to75° C. as can be noticed in Table 1. As shown in the Table, there is noelectrochemical evidence of any zinc oxidation and virtually nooxidation current existed when soluble sulfur, such as potassiumtetrasulfide, was added to the solution. In the above temperature range,it was found that the addition of sulfur completely passivates the zincand no electrochemical oxidation current was noticed.

EXAMPLE II

This example illustrates one set of experimental conditions, consistingof concentrated hydroxide, in which zinc oxidation to zinc sulfide canoccur despite the presence of dissolved sulfur. Several experiments werecarried out using concentrated hydroxide solutions, in which zincoxidation was found to occur despite the presence of dissolved sulfur.This is observed in the experimental measurements summarized in Table 2.Each experiment contained concentrated dissolved sulfur in solution (8mK₂S₄). As is apparent, when the solution contains 10.7 moles or higherKOH concentration, a significant discharge (oxidation) current in excessof 10 mA/cm² occurs. At a lower concentration of KOH, such as 9 molesper kg and less, no zinc oxidation occurred. At lower concentrations ofKOH such as 2.7 moles no zinc anodic oxidation occurred and a reduction(negative) current, destructive to the battery occurred.

TABLE 2 High hydroxide concentration will permit high zinc dischargecurrents in dissolved sulfur solutions. The oxidation current of planar99.9% zinc electrodes is measured at various applied potentials in 8molal K₂S₄ containing different concentrations of KOH at 50° C. The cellpotential (V_(cell)), in units of millivolts, mV, is determined relativeto a separate sulfur cathode. in 8 molal K₂S₄ and no KOH:   V_(cell)J_(Zn)   0 to 900 mV no Zn oxidation current, high reduction current. in8 molal K₂S₄ and 1 molal KOH:   V_(cell) J_(Zn)   0 to 900 mV no Znoxidation current, high reduction current. in 8 molal K₂S₄ and 3 molalKOH:   V_(cell) J_(Zn)   0 to 900 mV no Zn oxidation current, moderatereduction current. in 8 molal K₂S₄ and 9 molal KOH:   V_(cell) J_(Zn)  0 to 950 mV no Zn oxidation current, small reduction current. in 8molal K₂S₄ and 10 to 15 molal KOH:   V_(cell) J_(Zn)   0 to 950 mV highzinc oxidation current, no reductlon current. Zinc current, in units ofmA/cm², in 8 molal K₂S₄ and 9 to 15 molal KOH at 50° C.: V_(cell)J_(Zn)(9 m KOH) J_(Zn)(11 m KOH) J_(Zn)(13 m KOH) J_(Zn)(15 m KOH) 900−2 +1 −1 0 850 −1 +4 0 +2 800 0 +11 +5 +12 750 0 +13 +23 +26 100 0

EXAMPLE III

This example illustrates a second set of experimental conditions,consisting of dissolved hydrosulfide salts and dissolved hydroxidesalts, in which zinc oxidation can occur in the presence of a sulfurcontaining aqueous solution. As observed in Table 4, a hydrosulfide saltand hydroxide salt solution, such as 1 molal KHS with 4 molal KOH, canpermit a sustained zinc oxidation, although a lower current density thanin the pure hydroxide consisting of 3 molal KOH. Without being bound toany theory, this zinc oxidation KHS containing solution is achievedbecause KHS contains sulfur, but the sulfur is only in the reduced stateand cannot chemically react with Zn to form the insoluble passivatingZnS film. Therefore the anodic zinc oxidation can be sustained.

TABLE 3 Dissolved hydrosulfide and hydroxide will permit high zincdischarge currents. The oxidation current of planar 99.9% zincelectrodes is measured at various applied potentials at 50° C. The cellpotential (V_(cell)), in units of millivolts, (mV), is determinedrelative to a separate sulfur cathode. J_(Zn) is the oxidation currentmeasured on a planar zinc electrode. Zinc current, in units of mA/cm² at50° C.: V_(cell) J_(Zn)(3 m KOH) J_(Zn)(1 m KHS + 4 m KOH) 900 0 0 850+4 0 800 +25 +27 750 +50 +50

TABLE 4 High hydroxide will enhance zinc discharge currents inhydrosulfide containing solutions. The oxidation current of planar 99.9%zinc electrodes is measured at various applied potentials in 9 molal KHScontaining different concentrations of KOH at 50° C. The cell potential(V_(cell)), in units of millivolts, (mV), is determined relative to aseparate sulfur cathode. Zinc current, in units of mA/cm², in 8 molalKHS and 12 to 18 molal KOH at 50° C.: V_(cell) J_(Zn)(12 m KOH)J_(Zn)(15 m KOH) J_(Zn)(18 m KOH) 900 0 0 +1 850 +2 +2 +10 800 +5 +5 +15750 +12 +12 +22 700 +21 +27 +31

As summarized in Table 4, high zinc discharge currents are accomplishedeven in high concentration hydrosulfide solutions, and the magnitude ofthe zinc anodic current is enhanced with higher concentrations of KOH issolution.

EXAMPLE IV

This example illustrates conditions in which a zinc anode can be coupledwith a sulfur cathode to permit discharge of a zinc sulfur battery. Inthis example, various zinc sulfur battery discharges are attempted usinga planar zinc anode and a planar CoS electrocatalytic cathode, immersedin an aqueous solution containing sulfur. As illustrated by the solidtriangles in FIG. 2, the battery is completely inert to discharge in a 6molal KOH solution containing 0.64 g sulfur (dissolved as 7.3 molalK₂S₄) and 0.72 g KOH. In this cell, immediately following immersion ofthe electrodes into solution, a small open circuit voltage of 0.68 V isobserved which falls quickly, and under discharge load conditions, nocurrent occurs.

As illustrated by the curve containing the solid squares in FIG. 2, asmall, but significant, charge capacity can be sustained when the anodeis prevented from contact with the sulfur containing solutions. In thiscell, the anode is still in contact with a solution containing 0.72 gKOH, but sulfur is not in that solution. The 0.64 g sulfur is containedin a second solution in a second compartment also containing the CoSelectrode, and is separated from the zinc anode compartment. Theseparation is achieved by a membrane situated between the anode andcathode compartments which prevents anion movement, but permits cationmovement, such as the HD2291 membrane sold by Permion Company, N.Y. Inthis cell, discharge is sustained for 70 minutes, and this duration ofdischarge is attributed to the limited mass of KOH in the zinccompartment. As illustrated by the curve containing the solid circles inFIG. 2, in the two compartment zinc sulfur battery cell, a largecapacity can be sustained when the anode compartment is not limited inKOH mass. The anode contains a tenfold excess of KOH. Due to thesignificant increase in KOH mass, this cell has extended capacity.Discharge is sustained for 300 minutes, and this duration of dischargeis attributed to the limited mass of sulfur, 0.64 g, in the sulfurcompartment.

The final curve, the open squares, illustrates in FIG. 2 a singlecompartment cell, containing 0.64 g sulfur (dissolved as 7.3 molal K₂S₄)and again only 0.72 g KOH, However, in this case the KOH is present as14.3 molal KOH, so that zinc oxidation can occur despite contact withsolution phase sulfur. In this cell, an open circuit voltage of 0.74 Vis observed which is steady and represents a significant portion of thetheoretical voltage of a zinc sulfur battery described in equation 5. Inthis cell, the discharge capacity is considerably greater than the 6molal KOH inert cell, or the KOH mass limited cell, and approaches thatof the separated compartment excess KOH cell.

EXAMPLE V

This examples illustrates that the solid square discharge curveillustrated in FIG. 2 is limited and constrained by the charge containedin the 0.72 g KOH. In this two compartment cell, sulfur is not availablenear the anode, and in the absence of sulfur and without being bound toany theory, the two electron zinc anode oxidation is constrained by thenon-sulfur oxidation product:

Zn+4OH⁻→ZnO₂ ²⁻+H₂O+2e⁻  (7)

According to equation 4, each 4 moles of KOH will generate a maximum oftwo moles (equivalent to two faradays of charge at 96485 amp seconds ofcharge per faraday) during zinc oxidation. FIG. 3 illustrates thefraction of this charge, calculated from0.72 g KOH=0.128 moles KOH,attained during the 60 minute discharge of this two compartment zincsulfur battery. It is seen in the figure that approximately 90% of thisKOH limiting charge is generated by the cell during discharge.

EXAMPLE VI

This example illustrates that the solid circle discharge curveillustrated in FIG. 2 is limited and constrained by the charge containedin the 0.64 g sulfur. This two compartment cell contains an excess ofKOH according to equation 7, and the duration of discharge is limited bythe sulfur near the CoS electrode. Without being bound to any theory,according to equation 4, each mole of sulfur will generate a maximum oftwo moles during sulfur reduction. FIG. 4 illustrates the fraction ofthis charge, as calculated from 0.72 g KOH=0.128 moles KOH, attainedduring the 300 minute discharge of this two compartment zinc sulfurbattery, and it is seen in the Figure that over 90% of this KOH limitingcharge is generated by the cell during discharge.

EXAMPLE VII

This example illustrates that the open square discharge curveillustrated in FIG. 2 is limited and constrained by the charge containedin the 0.64 g sulfur, and not limited by the KOH mass. This onecompartment cell does effectively discharge for a long duration, despitethe presence of dissolved sulfur in contact with the zinc anode, anddespite the 0.72 g KOH which limited a discharge duration in the twocompartment cell. Duration of discharge is limited by the sulfur presentnear the CoS electrode. As illustrated in FIG. 5, each mole of sulfurgenerates approximately 80% of the maximum of two moles during sulfurreduction. This extended discharge precludes the possibility of ZnO₂ ²⁻as the discharge product and therefore, without being bound to anytheory, the extended discharge can be ascribed to the process given byequation 5. It seems that, the concentrated hydroxide permits aneffective zinc oxidation, as described by equation 3, despite zinccontact with aqueous sulfur. The resultant zinc sulfur battery combinesthe attributes of the low mass, high storage capacity cell, available ina single compartment configuration cell, with the attribute of higheffective discharge current available in the two compartmentconfiguration cell.

What is claimed is:
 1. A battery comprising two half-cells which arepositioned in electrochemical contact with one another through anaqueous solution, wherein one of said half-cells comprises a zinc anodeand the second half-cell comprises an aqueous solution of a concentratedmetal cation hydrosulfide salt, a concentrated metal cation hydroxidesalt and a reducible sulfur in an amount of at least 0.01 moles per kg,being positioned in an electron transferring contact with a currenttransferring electrocatalytic electrode.
 2. The battery according toclaim 1, wherein the zinc anode is selected from a high surface area anda low surface area.
 3. The battery according to claim 1, wherein saidzinc anode is selected from a zinc alloy containing at least 92% to 99%purity of zinc metal.
 4. The battery according to claim 1, wherein saidmetal cation hydrosulfide is selected from an alkali hydrosulfide havinga general formula MHS, wherein M is an alkali cation.
 5. The batteryaccording to claim 1, wherein the cation in said hydrosulfide salt isselected from one of the groups IIA, IIIA, IVA, VA, transition metalsand hydrogen.
 6. The battery of claim 1, wherein said solution containsa hydrosulfide salt in an amount over 0.1 mole per kg.
 7. The batteryaccording to claim 6, wherein said solution contains a hydrosulfide saltin an amount of more than one mole per kg.
 8. The battery according toclaim 6, wherein said solution contains a hydrosulfide salt in an amountof over 9 moles per kg.
 9. The battery according to claim 1, whereinsaid metal cation hydroxide is selected from an alkali hydroxide havingthe general formula MOH.
 10. The battery according to claim 1, whereinthe cation in said hydroxide salt is selected from the group IIA, IIIA,IVA and VA.
 11. The battery according to claim 1, wherein the solutionin said electrolyte contains up to 1 mole per kg of hydroxide salt. 12.The battery according to claim 1, wherein said solution contains ahydroxide salt in an amount over 1 mole per kg.
 13. The batteryaccording to claim 1, wherein said solution contains a hydroxide salt inan amount of over 9 moles per kg.
 14. The battery according to claim 1,wherein the cell contains means to impede a transfer of the reactivesulfur between said zinc anode and sulfur present in said other halfcell.
 15. The battery according to claim 14, wherein said means areselected from a membrane, ceramic frit and an agar solution, located ina position which separate said half cells.
 16. The battery according toclaim 1, which is rechargeable by application of a voltage in excess ofthe discharge cell open circuit potential.
 17. The battery according toclaim 1, wherein a portion of said reducible sulfur is in the form ofundissolved solid sulfur in the surrounding of the cell.
 18. A batterycomprising two half-cells positioned in electrochemical contact with oneanother through the aqueous solution of concentrated metal cationhydrosulfide salt, metal cation hydroxide salt and reducible sulfur ofclaim 1.